This removes the std folder from the tree.
Various parts of the tests are pretty tightly dependent
on std (47 direct imports and 75 indirect imports, not
counting the cli tests that use them as fixtures) so I've
added std as a submodule for now.
All benchmarks are done in Rust and can be invoked with
`cargo bench`.
Currently this has it's own "harness" that behaves like
`./tools/benchmark.py` did.
Because of this tests inside `cli/bench` are currently not run.
This should be switched to the language provided harness
once the `#[bench]` attribute has been stabilized.
